Rodless cylinders of the prior art comprise an elongated cylinder member containing a piston which is movable within the cylinder from one end to the other. This movement is responsive to the introduction of pressurized fluid into the cylindrical member. A flexible cable is secured to each end of the piston, each cable passing through seals in the ends of the cylinders and around a pulley at each end of the cylinder with the outer ends of the cables being secured to opposite sides of a drive block. U.S. Pat. No. 4,057,257 which issued on Nov. 8, 1977 to Tol-O-Matic Inc. is representative of this type of prior art. Various types of guides are utilized for supporting the reciprocating drive block, these either resting upon the outer wall of the cylinder or being separate guides supported away from the cylinder.
The cables which transfer the motion from the piston to the drive block must be kept under a slight tension so that during use the mechanism operates precisely with no slack occurring in either of the cables. The operation of a rodless cylinder is very rapid and there is little cushioning effect at the ends of the stroke with the result being that excessively large forces have to be contended with after the rapid acceleration of the cylinder from a stationary position. Large tension loads in the cables are therefore encountered which stretch the cables during use. The effects of such stretching cannot be tolerated and therefore an adjustment mechanism is required so that the cables can be periodically tensioned.
Also, rodless cylinders are often located in a dirty environment which leads to premature wear of the guides which support the reciprocating drive block and also of the cables and pulleys.